1. Field of the Invention
The present invention relates to wireless communication systems. More particularly, the present invention relates to the design of downlink control information formats scheduling data transmissions to or data receptions from User Equipment (UE) with limited capabilities.
2. Description of the Art
A communication system includes a DownLink (DL) that conveys transmission signals from transmission points such as Base Stations (BS or NodeBs) to User Equipments (UEs), and an UpLink (UL) that conveys transmission signals from UEs to reception points such as NodeBs. A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a cellular phone, a personal computer device, and the like. A NodeB, which is generally a fixed station, may also be referred to as an access point or other equivalent terminology.
DL signals includes data signals, which carry the information content, control signals, and Reference Signals (RSs), which are also known as pilot signals. A NodeB conveys data information to UEs through respective Physical Downlink Shared CHannels (PDSCHs) and control information through respective DL Control CHannels (CCHs). Multiple RS types may be supported, such as for example a Common RS (CRS) transmitted over substantially the entire DL BandWidth (BW) BW and the DeModulation RS (DMRS) transmitted in a same BW as an associated PDSCH.
UL signals also include data signals, control signals and RSs. UEs convey data information to NodeBs through respective Physical Uplink Shared CHannels (PUSCHs) and control information through respective Physical Uplink Control CHannels (PUCCHs). A UE transmitting data information may also convey control information through a PUSCH. The RS may be a DMRS or a Sounding RS (SRS) which a UE may transmit independently of a PUSCH.
FIG. 1 is a diagram illustrating a structure for a DownLink (DL) Transmission Time Interval (TTI) according to the related art.
Referring to FIG. 1, a DL TTI includes one subframe 110 which includes two slots 120 and a total of NsymbDL symbols used for transmitting data information, DL Control Information (DCI), or RS. The first MsymbDL symbols are used to transmit DL CCHs 130. The first MsymbDL symbols may be dynamically indicated in each DL TTI through a Physical Control Format Indicator CHannel (PCFICH). The remaining NsymbDL-MsymbDL symbols are primarily used to transmit PDSCHs 140. The transmission BW includes frequency resource units referred to as Resource Blocks (RBs). Each RB includes NscRB sub-carriers, or Resource Elements (REs), and a UE can be allocated MPDSCH RBs for a total of MscPDSCH=MPDSCH·NscRB REs for a PDSCH transmission BW in a DL TTI. Some REs in some symbols contain CRS (or DMRS) 150 which enable channel estimation and coherent demodulation of data signals or control signals at a UE. A PDSCH transmission in a second slot may be at a same BW or at a different BW than in a first slot. In the former case, the PDSCH transmission is referred to as localized. In contrast, in the latter case the PDSCH transmission is referred to as distributed.
A PDSCH transmission to a UE or a PUSCH transmission from a UE may be scheduled by a NodeB through a transmission of a respective Physical DL Control CHannel (PDCCH) conveying a DCI format which provides information for a respective PDSCH or PUSCH transmission as it is subsequently described. A PDSCH or a PUSCH transmission may also be Semi-Persistently Scheduled (SPS) by a NodeB through higher layer signaling, such as Radio Resource Control (RRC) signaling, in which case it occurs at predetermined TTIs and with predetermined parameters specified by the higher layer signaling.
To avoid a PDCCH transmission to a UE that is blocking a PDCCH transmission to another UE, a location of each PDCCH transmission in the time-frequency domain of a DL control region is not unique. Therefore, a UE may perform multiple decoding operations per DL subframe to determine whether there are PDCCHs intended for the UE in a DL subframe. The resource unit for a PDCCH transmission is referred to as a Control Channel Element (CCE) and includes multiple REs. For a given number of DCI format bits, a number of CCEs for a respective PDCCH depends on a channel coding rate (Quadrature Phase Shift Keying (QPSK) is assumed as the modulation scheme). A NodeB may use a lower channel coding rate (e.g., more CCEs) for transmitting a PDCCH to a UE experiencing low DL Signal to Interference and Noise Ratio (SINR) than to a UE experiencing a high DL SINR. The CCE Aggregation Levels (ALs) may include, for example, 1, 2, 4, and 8 CCEs.
A NodeB may also transmit ACKnowledgement information associated with a Hybrid Automatic Repeat reQuest (HARQ) process (HARQ-ACK information) for transmission of data Transport Blocks (TBs) in respective PUSCHs. HARQ-ACK signals through respective Physical Hybrid-ARQ Indicator CHannels (PHICHs) inform respective UEs whether transmissions of respective data TBs were correctly or incorrectly detected by a NodeB. For a PUSCH transmission scheduled by PDCCH, the PHICH resource nPHICH can be assumed to be derived as in Equation (1)nPHICH=ƒ(IPRB_RAlowest_ind ex,nDMRS,NPHICH)  (1)where ƒ(·) is a function of a first UL RB IPRB_RAlowest_index for a respective PUSCH, of a nDMRS parameter provided in a DCI format scheduling the PUSCH as it is subsequently described, and of other parameters. NPHICH is informed to a UE through higher layer signaling by a NodeB. For a SPS PUSCH, a PHICH resource can be assigned to a UE through higher layer signaling.
The DL control region in FIG. 1 uses a maximum of MsymbDL=3 subframe symbols, and a PDCCH is transmitted substantially over a total DL BW. As a consequence, such control region has limited capacity and cannot achieve interference coordination in the frequency domain. Expanded PDCCH capacity or PDCCH interference coordination in the frequency domain is needed in several cases. One such case is an extensive use of spatial multiplexing for PDSCH transmissions in which multiple DL SAs schedule same PDSCH resources to respectively multiple UEs. Another case is for heterogeneous networks in which DL transmissions in a first cell experience strong interference from DL transmissions in a second cell and DL interference co-ordination in the frequency domain between the two cells is needed.
A direct extension of a DL control region as in FIG. 1 to more than MsymbDL=3 subframe symbols is not possible at least due to a requirement to support UEs which cannot be aware of such extension. An alternative is to support DL control signaling in a PDSCH region according to the related art by using individual RBs to transmit control signals. A PDCCH transmitted in RBs of a PDSCH region according to the related art will be referred to as Enhanced PDCCH (EPDCCH).
FIG. 2 is a diagram illustrating EPDCCH transmissions in a DL subframe according to the related art.
Referring to FIG. 2, although EPDCCH transmissions start immediately after a DL control region 210 according to the related art and are over all remaining subframe symbols, EPDCCH transmissions may instead always start at a fixed location, such as the fourth subframe symbol, and extend over a part or all of the remaining subframe symbols. EPDCCH transmissions occur in four RBs, 220, 230, 240, and 250, while remaining RBs can be used to transmit PDSCHs 260, 262, 264, 266, and 268. An enhanced PCFICH (EPCFICH) or an Enhanced PHICH (EPHICH) may also be supported. In a DL TTI, an Enhanced Control CHannel (ECCH), referring to an EPDCCH, an EPCFICH, or an EPHICH, may be transmitted in a same RB, in which case the ECCH is referred to as localized, or over multiple RBs, in which case the ECCH is referred to as distributed.
Demodulation of information conveyed by an EPDCCH may be based on a CRS or on a DMRS. A DMRS is transmitted in some subframe symbols and in a subset of REs in RBs used for an associated EPDCCH transmission.
FIG. 3 is a diagram illustrating a DMRS structure in a RB over a DL TTI according to the related art.
Referring to FIG. 3, the DMRS REs 310 are placed in some subframe symbols of a RB used to transmit an ECCH. For orthogonal multiplexing of different DMRS, a first DMRS transmission is assumed to use an Orthogonal Cover Code (OCC) of {1, 1} over two respective REs that are located in a same frequency position and are successive in the time domain while a second DMRS transmission is assumed to use an OCC of {1, −1}.
FIG. 4 is a diagram illustrating an encoding and transmission process for a DCI format according to the related art.
Referring to FIG. 4, a NodeB separately encodes and transmits each DCI format in a respective PDCCH or EPDCCH. A Radio Network Temporary Identifier (RNTI) for a UE, for which a DCI format is intended for, masks a Cyclic Redundancy Check (CRC) of a DCI format codeword in order to enable the UE to identify that a particular DCI format is intended for the UE. The CRC of (non-coded) DCI format bits 410 is computed using a CRC computation operation 420, and the CRC is then masked using an exclusive OR (XOR) operation 430 between CRC and RNTI bits 440. The XOR operation 430 is defined as: XOR(0,0)=0, XOR(0,1)=1, XOR(1,0)=1, XOR(1,1)=0. The masked CRC bits are appended to DCI format information bits using a CRC append operation 450, channel coding is performed using a channel coding operation 460, for example using a Tail Biting Convolutional Code (TBCC), followed by rate matching operation 470 applied to allocated resources, and finally, an interleaving and a modulation 480 operation, after which the output control signal 490 is transmitted. In the present example, both a CRC and a RNTI include 16 bits.
FIG. 5 is a diagram illustrating a reception and decoding process for a DCI format according to the related art.
Referring to FIG. 5, a UE receiver performs the reverse operations of a NodeB transmitter to determine whether the UE has a DCI format assignment in a DL subframe. A received control signal 510 is demodulated and the resulting bits are de-interleaved at operation 520, a rate matching applied at a NodeB transmitter is restored through operation 530, and control data is subsequently decoded at operation 540. After decoding the control data, DCI format information bits 560 are obtained after extracting CRC bits 550 which are then de-masked 570 by applying the XOR operation with a UE RNTI 580. Finally, a UE performs a CRC test 590. If the CRC test passes, a UE detects a DCI format and determines parameters for signal reception or signal transmission. If the CRC test does not pass, a UE disregards a presumed DCI format.
FIG. 6 is a diagram illustrating a PUSCH transmission structure over an UL TTI according to the related art.
Referring to FIG. 6, an UL TTI includes one subframe 610 which includes two slots. Each slot 620 includes NsymbUL symbols 630 used for transmitting data information, UL Control Information (UCI), or RS. A PUSCH transmission in one slot may be either at a same BW or at a different BW than a PUSCH transmission in the other slot. Some symbols in each slot are used to transmit RS 640 which enables channel estimation and coherent demodulation of received data information and/or UCI at a NodeB. A UE is allocated MPUSCH RBs 650 for a total of MscPUSCH=MPUSCH·NscRB REs for a PUSCH transmission BW. The last subframe symbol may be used for SRS transmission 660 from one or more UEs. The main purpose of a Sounding Reference Signal (SRS) is to provide a NodeB with an estimate for a UL channel medium experienced by a respective UE. SRS transmission parameters for each UE are configured by a NodeB through higher layer signaling.
A UE transmits UCI to provide a NodeB information related to PDSCH transmissions to the UE or PUSCH transmissions from the UE. UCI includes HARQ-ACK information regarding a correct or incorrect detection of data TBs, Channel State Information (CSI) for a DL channel a UE experiences, and a Service Request (SR) informing a NodeB that a UE has data to transmit. A UE transmitting PUSCH may also provide a NodeB with a Buffer Status Report (BSR) informing a NodeB of an amount of data a UE has for transmission in its buffer.
FIG. 7 is a diagram illustrating a PUCCH structure for HARQ-ACK signal transmission according to the related art.
Referring to FIG. 7, HARQ-ACK signals and RS enabling coherent demodulation of HARQ-ACK signals are transmitted in one slot 710 of a PUCCH subframe including 2 slots. The transmission in the other slot can be at a different part of an UL BW. HARQ-ACK information bits 720 modulate 730 a Zadoff-Chu (ZC) sequence 740, for example using Binary Phase Shift Keying (BPSK) for 1 HARQ-ACK bit or QPSK for 2 HARQ-ACK bits, which is then transmitted after performing a Inverse Fast Fourier Transform (IFFT) operation 750. Each RS 760 is transmitted using an unmodulated ZC sequence.
For an UL system BW of NRBUL RBs, a ZC sequence ru,v(α)(n) is defined by a Cyclic Shift (CS) α of a base ZC sequence ru,v(n) according to ru,v(α)(n)=ejαnru,v(n), 0≤n<MscRS, where MscRS=mNscRB is the length of the ZC sequence, 1≤m≤NRBUL, and ru,v(n)=xq(n mod NZCRS) where the qth root ZC sequence is defined by
                    x        q            ⁡              (        m        )              =          exp      ⁡              (                                            -              j                        ⁢                                                  ⁢            π            ⁢                                                  ⁢            q            ⁢                                                  ⁢                          m              ⁡                              (                                  m                  +                  1                                )                                                          N            ZC            RS                          )              ,0≤m≤NZCRS−1 with q given by q=└q+½┘+v·(−1)└2q┘ and q given by q=NZCRS·(u+1)/31. The length NZCRS of a ZC sequence is given by the largest prime number such that NZCRS<MscRS. Multiple RS sequences can be defined from a single base sequence through different values of α. A PUCCH is assumed to be transmitted in one RB (MscRS=NscRB).
FIG. 8 is a diagram illustrating a transmitter for a ZC sequence according to the related art.
Referring to FIG. 8, a mapper 820 maps a ZC sequence 810 to REs of an assigned transmission BW as REs of the assigned transmission BW are indicated by RE selection unit 825. An IFFT is then performed by IFFT unit 830, a CS is applied to the output by CS unit 840, followed by scrambling with a cell-specific sequence using scrambler 850. A resulting signal is filtered by filter 860, a transmission power is applied by power amplifier 870, and a ZC sequence is transmitted 880. As an example, the reverse operations are performed at a NodeB receiver. Without modulation, a ZC sequence serves as a RS. With modulation, a ZC sequence serves as a HARQ-ACK signal or as a CSI signal. The SR may be transmitted using an unmodulated ZC sequence through On-Off Keying.
Different CSs of a ZC sequence provide orthogonal ZC sequences. Therefore, different CSs α of a same ZC sequence can be allocated to different UEs in a same PUCCH RB and achieve orthogonal multiplexing for transmissions of HARQ-ACK signals or of CSI signals, and RS. For a RB including NscRB=12 REs, there are 12 different CS. The number of usable CS depends on the channel dispersion characteristics and can typically range between 3 and 12. Orthogonal multiplexing can also be in the time domain using OCC where PUCCH symbols conveying a same signal type in each slot are multiplied with elements of an OCC. For example, for the structure in FIG. 7, an HARQ-ACK signal in each slot can be modulated by a length-4 OCC, such as a Walsh-Hadamard (WH) OCC, while a RS in each slot can be modulated by a length-3 OCC, such as a DFT OCC. In this manner, the multiplexing capacity per RB per subframe is increased by a factor of 3 (e.g., determined by the OCC with the smaller length Noc).
A UE may implicitly determine a PUCCH resource, nPUCCH, for HARQ-ACK signal transmission, in response to a PDSCH reception scheduled by a PDCCH, based on a first CCE, nCCE, used to transmit the PDCCH as in Equation (2)nPUCCH=nCCE+NPUCCH  (2)where NPUCCH is an offset informed to the UE by the NodeB through higher layer signaling. The PUCCH resource provides a CS and an OCC at an RB for HARQ-ACK signal transmission. For SPS PDSCH, a PUCCH resource for HARQ-ACK signal transmission may be assigned to a UE by a NodeB through higher layer signaling.
Encoding of DCI is based on a TBCC while encoding of data information is based on a turbo code. This is due to the better performance of a TBCC for payloads less than about 100 bits, such as the TBCC included in DCI formats, and the better performance of a turbo code for payloads above about 100 bits, such as the TBCC included in data TBs.
FIG. 9 is a diagram providing a detection performance for a TBCC and for a turbo code according to the related art.
Referring to FIG. 9, the detection performance is provided in terms of required SNR to achieve a target BLock Error Rate (BLER) of 0.01 which is typically used for DCI, as a function of the payload assuming a coding rate of ⅓. In general, as a target BLER increases, a number of bits for which a TBCC outperforms a turbo code decreases. For example, although not illustrated for brevity, for a target BLER of 0.1 which is typically used for detection of data information, a TBCC outperforms a turbo code for payloads smaller than about 70-80 bits.
A DCI format scheduling a PDSCH or a PUSCH includes several Information Elements (IEs). Different DCI formats may be associated with different PDSCH or PUSCH Transmission Modes (TMs) configured to a UE. For example, a first DCI format can be used to schedule a transmission of only one data TB to or from a UE while a second DCI format can be used to schedule a transmission of up to two data TBs. Exemplary embodiments of the present invention focus on DCI formats associated with one data TB and on a DCI format scheduling PDSCH having a same size as a DCI format scheduling PUSCH.
Table 1 provides IEs for a DCI format scheduling a PUSCH for a maximum of one data TB.
TABLE 1IEs of a DCI Format Scheduling PUSCH (DCI Format 0)IENumber of BitsDifferentiation Flag for10/1ARA┌log2(NRBUL(NRBUL + 1)/2)┐FH Flag1MCS and RV5NDI1TPC Command for2PUSCHCS and OCC Index nDMRS3CSI Request1SRS Request1DAI (TDD)0 (FDD) or 2 (TDD)UL Index (TDD)0 (FDD) or 2 (TDD)Padding Bits for 0 = 1A1RNTI16 Total43 (FDD) or 47 (TDD)
A differentiation flag IE indicates one of two DCI formats, DCI format 0 and DCI format 1A, having a same size. For example, a value of zero indicates DCI format 0 and a value of one indicates DCI format 1A.
A Resource Allocation (RA) IE indicates a part of an UL BW for a PUSCH transmission. A UE is allocated a number of consecutive RBs and for an UL BW including NRBUL, the possible RB allocations can be represented by ┌ log2(NRBUL(NRBUL+1)/2)┐ bits where ┌·┐ is the ceiling function which rounds a number to the next greater integer.
A Frequency Hopping (FH) flag IE indicates whether the PUSCH transmission is in a same BW or in a different BW in a second slot relative to a first slot.
A Modulation and Coding Scheme (MCS) and a Redundancy Version (RV) IE provides, through one of a first number of states, a modulation scheme (QPSK, QAM16, QAM64) and a code rate of a turbo code for a transmission of a data TB. In a case of a data TB retransmission according to a physical layer HARQ process, this RV IE provides through one of the remaining number of states the RV for an Incremental Redundancy (IR) assumed to be apply using turbo encoding assuming non-adaptive HARQ retransmissions (e.g., same MCS as the initial transmission for a same data TB).
A New Data Indicator (NDI) IE informs a UE as to whether a data TB the UE should transmit is a new one or whether the data TB corresponds to a retransmission of a previous data TB (e.g., a synchronous HARQ process is assumed for PUSCH transmissions).
A CS and OCC index IE, nDMRS, informs a UE of a CS and OCC the UE should apply to a DMRS transmission.
A CSI request IE informs a UE whether the UE should include CSI feedback in a PUSCH transmission.
A SRS request IE informs the UE whether the UE should transmit an SRS according to a configured set of SRS transmission parameters (e.g., the other state indicates no SRS transmission). The SRS transmission parameters include the SRS transmission BW, the CS of the respective ZC sequence, the starting BW position of the transmission, and so on.
For a TDD system, two more IEs are included in DCI formats scheduling PUSCH transmissions. A first IE is a Downlink Assignment Index (DAI) IE informing a UE of a number of PDSCH transmissions to the UE within a bundling window which is defined as a number of DL subframes for which a UE provides HARQ-ACK feedback to a NodeB in a same UL subframe. Based on the DAI value, a UE determines a number of HARQ-ACK bits, if any, the UE includes in a PUSCH transmission. A second IE is an UL index IE which informs a UE of an UL subframe for a PUSCH transmission. This is applicable to TDD configurations of UL-DL subframes having more UL subframes than DL subframes. The partitioning of UL-DL subframes is periodic per frame and a frame may include, for example, 10 subframes.
Finally, padding bits may be included in DCI format 0, if applicable, in order to make its size equal to that of DCI format 1A.
Table 2 provides IEs for a DCI format scheduling a PDSCH for a maximum of one data TB.
TABLE 2IEs of a DCI Format Scheduling PUSCH (DCI Format)IENumber of BitsDifferentiation Flag for 0/1A1RA┌log2(NRBDL(NRBDL + 1)/2)┐Distributed/Localized1Transmission (FH) FlagMCS5NDI1RV2HARQ Process Number3 (FDD) or 4 (TDD)TPC Command for PUCCH2SRS Request1DAI (TDD)0 (FDD) or 2 (TDD)Padding Bits for 0 = 1A0RNTI16 Total (FDD)43 
The functionality and size of a differentiation flag IE, a RA flag IE, a distributed/localized flag IE, an MCS IE, a NDI IE, and a SRS IE are same as for DCI format 0, and this also holds for the padding bits. Asynchronous HARQ is assumed for PDSCH transmissions and a RV is provided by a separate IE while an MCS IE provides only MCS information.
A HARQ process number IE is included in DCI formats scheduling PDSCH transmissions to support an asynchronous HARQ process.
A Transmit Power Control (TPC) command IE provides a TPC command for a UE to adjust a power of an HARQ-ACK signal transmitted in a PUCCH in response to a PDSCH reception by a UE.
A DAI IE provides a counter for a number of PDSCH transmissions to a UE in a bundling window. Using a DAI IE, a UE can identify missed PDSCH receptions, due to respective missed PDCCH detections within a bundling window, unless a UE does not detect a PDCCH in any subsequent subframe after one or more subframes of missed PDCCHs.
UEs may be able to communicate over an entire system BW and with large data TB Sizes (TBS) or over only a part of a system BW and with limited data TBS. In the former case, UEs can benefit from most or all capabilities of a network for PDSCH receptions or PUSCH transmissions, are typically used by humans, and will be referred to as conventional UEs. In the latter case, UEs have substantially reduced capabilities compared to UEs according to related art in order to substantially reduce their cost, are typically associated with machines, and will be referred to as Machine Type Communication (MTC) UEs.
MTC UEs are low cost devices targeting various low data rate traffic applications including smart metering, intelligent transport systems, consumer electronics, and medical devices. Typical traffic patterns from MTC UEs are characterized by low duty cycles and small data packets (e.g., small TBS) in the order of a few tens or a few hundred bytes. MTC UEs are typically low mobility but high mobility UEs, such as for example motor vehicles, also exist. Also, unlike UEs according to the related art, MTC UEs generate more UL traffic than DL traffic and a majority of DL traffic is higher layer control information for configuration.
Unlike UEs according to the related art, such as for example a smart-phone, which may have many features, MTC UEs may have only a minimum of necessary features. Accordingly, the modem becomes the primary contributor to the cost of an MTC UE. Therefore, main cost drivers for MTC UEs are the Radio Frequency (RF) components and the Digital Base-Band (DBB) components mainly for the receiver. The RF components include a power amplifier, filters, a transceiver radio chains, and possibly a duplexer (for full duplex FDD operation). The DBB components of a UE receiver include a channel estimator, a channel equalizer, a PDCCH decoder, a PDSCH decoder, and a subframe buffer. For example, a channel estimator may be based on a Minimum Mean Square Error (MMSE) estimator, a channel equalizer may be an FFT, a PDCCH decoder may be a decoder for a TBCC, and a data decoder may be a decoder for a Turbo Code (TC).
RF costs are related to implementation and production methods as well as to design choices. For example, considering economies of scale, it may be more cost effective to use a same amplifier for conventional UEs and for MTC UEs (e.g., this will also ensure the same UL coverage) while a number of transmitter antennas for MTC UEs may be limited to one.
DBB costs are related to the communication capabilities of MTC UEs and are dominated by the receiver complexity which is typically about an order of magnitude larger than the transmitter complexity. As channel estimator complexity, FFT complexity, and subframe buffering requirements are directly associated to a reception BW, DL transmissions to MTC UEs may be over a smaller BW, at least in the DBB, than DL transmissions to conventional UEs. For example, DL transmissions to MTC UEs may be over a 1.4 MHz BW at the DBB while DL transmissions to conventional UEs may be over a 20 MHz BW.
A complexity of a PDCCH decoder depends on a number of decoding operations an MTC UE performs per subframe. As MTC UEs do not need to support a same number of TMs as conventional UEs, for example MTC UEs may not need to support spatial multiplexing for PDSCH receptions or PUSCH transmissions, a maximum number of decoding operations an MTC UE needs to perform per subframe can be significantly smaller than that for a conventional UE. A complexity of a PDSCH decoder depends on a maximum supportable TBS. Allowing for a relatively small maximum TBS for MTC UEs limits an associated decoder complexity.
MTC UEs are assumed to access a communication system in a same manner as conventional UEs. Synchronization signals are first acquired to establish synchronization with a NodeB followed by a detection of a Broadcast CHannel (BCH) that conveys essential information for subsequent communication between a NodeB and UEs (e.g., conventional UEs or MTC UEs). Regardless of a DL BW of a communication system, synchronization signals and BCH are assumed to be transmitted over a minimum DL BW located in the center of a DL BW of a communication system, such as for example in a middle six RBs of a DL BW, and over a number of Orthogonal Frequency Division Multiplexing (OFDM) symbols in a subframe. After establishing communication with a NodeB, a different part of a DL BW may be allocated to an MTC UE.
One aspect of supporting communication for MTC UEs is a design of DCI formats scheduling PDSCH transmissions to or PUSCH transmissions from MTC UEs. Respective TMs and a number of decoding operations for PDCCHs carrying respective DCI formats should be defined with an objective of minimizing DBB complexity while providing desired functionalities. It is desirable for MTC UEs to perform a smaller number of decoding operations than conventional UEs without impacting an associated scheduling efficiency and functionality.
Another aspect is a reduction in a PDCCH overhead associated with scheduling PDSCH transmissions to or PUSCH transmissions from MTC UEs. As TBS conveyed to or from MTC UEs can be significantly smaller than TBS conveyed to or from conventional UEs, similar reductions in a PDCCH overhead are needed for efficient operation of a communication system.
Finally, as communication with MTC UEs is typically UL intensive and a DBB receiver complexity is significantly larger than a DBB transmitter complexity, a more efficient coding method can be used for data transmission from MTC UEs in a PUSCH than for data transmission to MTC UEs in a PDSCH.
Therefore, there is a need to design transmissions modes and respective DCI formats associated with PDSCH transmissions to or PUSCH transmissions from MTC UEs.
There is another need to reduce a PDCCH overhead associated with scheduling PDSCH transmissions to or PUSCH transmissions from MTC UEs.
In addition, there is another need to define different coding methods for data transmitted to an MTC UE than for data transmitted from an MTC UE.
Therefore, a need exists for an apparatus, system, and method for designing transmissions modes and respective DL Control Information (DCI) formats associated with PDSCH transmissions to MTC UEs or PUSCH transmissions from MTC UEs, reducing a PDCCH overhead associated with scheduling PDSCH transmissions to MTC UEs or PUSCH transmissions from MTC UEs, and defining different coding methods for data transmitted to an MTC UE than for data transmitted from an MTC UE
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.